Nutrition-enhanced foods. Rice given a beta-carotene gene already has been developed in hopes of preventing blindness among children in countries where vitamin-A deficiency is common.

Anti-allergy genes. It may be possible to genetically alter foods such as peanuts to reduce their dangerous allergy-causing capability.

Pest-resistant crops. They're given genes that help repel or kill insects or viruses, reducing pesticide use. Some, such as corn, have been planted commercially for several years. Others are in the works.

Herbicide-resistant crops. With these, a herbicide will kill weeds but not the crop.

Faster-ripening crops. Tomatoes are given genes to help them ripen on the vine.

Critics' concerns:

Allergic reactions to transferred genes. As far as anyone knows, this hasn't occurred with any existing biotech crop. But scientists say transferring protein genes into a food from peanuts or shrimp, for example, might cause reactions in people allergic to those things.

Regulations are needed to prevent this problem, says Ronald Phillips, widely known biotech researcher at the University of Minnesota. The FDA requires that labels list common allergens such as peanuts as an ingredient if genes from them have been transferred into another food.

Long-term, unpredicted health impacts. Pinpointing cause and effect could be nearly impossible. Critics say science needs to know more before pushing biotech foods on a massive scale. Advocates point to possible harmful effects of pesticides, whose use is reduced with biotech crops.

Tough bugs. Insects or bacteria might become resistant to bug-fighting biotech crops, creating bugs that are even more destructive.

Tough weeds. Pollen drift from a biotech crop could alter related wild plants, perhaps creating "super weeds." Scientists are researching answers, but each situation could require a different solution.

Drug drift. Pollen from drug-bearing plants, such as those containing a vaccine gene, might cross-pollinate other plants. Scientists are studying how much crop isolation is needed to prevent this.